Finite Element Modeling of Magnitude and Location of Brain Micromotion Induced Strain for Intracortical Implants

Micromotion-induced stress remains one of the main determinants of life of intracortical implants. This is due to high stress leading to tissue injury, which in turn leads to an immune response coupled with a significant reduction in the nearby neural population and subsequent isolation of the implant. In this work, we develop a finite element model of the intracortical probe-tissue interface to study the effect of implant micromotion, implant thickness, and material properties on the strain levels induced in brain tissue. Our results showed that for stiff implants, the strain magnitude is dependent on the magnitude of the motion, where a micromotion increase from 1 to 10 μm induced an increase in the strain by an order of magnitude. For higher displacement over 10 μm, the change in the strain was relatively smaller. We also showed that displacement magnitude has no impact on the location of maximum strain and addressed the conflicting results in the literature. Further, we explored the effect of different probe materials [i.e., silicon, polyimide (PI), and polyvinyl acetate nanocomposite (PVAc-NC)] on the magnitude, location, and distribution of strain. Finally, we showed that strain distribution across cortical implants was in line with published results on the size of the typical glial response to the neural probe, further reaffirming that strain can be a precursor to the glial response.

Self-Assembling Flexible 3D-MEAs for Cortical Implants

Flexible Multi Electrode Arrays (MEAs) for neural interfacing reduce the mechanical mismatch between the soft brain tissue and the electrode arrays allowing accurate signal recordings and neural stimulation while reducing inflammatory responses. Many standard manufacturing processes of MEAs are designed for planar structures and the production of three-dimensional structures is challenging. In the present study, shaft structures with one to two circular gold microelectrodes (10 - 20 μm), each on a base polyimide (PI) substrate, were investigated. We describe a fabrication method, with which shafts made from bi-layer PI flip into the third dimension, which is a first step towards spontaneous assembly of electrodes in flexible 3D MEAs for neuroelectronic applications. A lift-up of the shafts was achieved by the contraction of a second PI layer and a steady nitrogen flow during polycondensation. This shrinking PI was structured in pits with a width of 5 - 600 μm. We achieved liftup angles of up to 42 degrees. The shaft structures can be hardened and later be used for neural implantation experiments.

Basal Implant: A Remedy to Restore Resorbed Alveolar Ridges

The conventional crestal implants are used only when there is adequate jawbone height and width. Results of conventional implants are good in patients with healthy bone at the time of treatment, but prognosis gets deteriorated when surgical augmentation of bone is included with implant placement. These augmentation procedures have surgical risks and are costlier to the patients. Patients with atrophied jawbones are given no treatment, until crestal implants are seen as the last option. In this article, the indications for basal implants and functional differences between basal implants and crestal implants have been discussed.Patients with extreme jawbone atrophy do not benefit from crestal implants. The basal bone is the (cortical) osseous tissue of the mandible and maxilla, and lies below the alveolar process, which has a relatively strong and no resorbing framework.Basal osseointegrated and basal cortical screw (BCS) are two types of implants designed to take anchorage from the cortical bone of the jaw. BCS implants have long shafts and can be placed immediately in the socket after extraction and provided with immediate loading within 72 hours of implant placement. Basal implants are also called bicortical or cortical implants as they utilize the cortical portion of the jawbones for anchorage and implant stability. The basal bone has better quality and quantity of cortical bone for retention of these unique and highly advanced implants. The other names for these implants are lateral implants or disk implants.

Automatic Identification and Avoidance of Axon Bundle Activation for Epiretinal Prosthesis

ABSTRACTRetinal prostheses must be able to activate cells in a selective way in order to restore high-fidelity vision. However, inadvertent activation of far-away retinal ganglion cells (RGCs) through electrical stimulation of axon bundles can produce irregular and poorly controlled percepts, limiting artificial vision. Therefore, the problem of axon bundle activation can be defined as the axonal stimulation of RGCs with unknown soma and receptive field locations, typically outside the electrode array. Here, a new algorithm is presented that utilizes electrical recordings to determine the stimulation current amplitudes above which bundle activation occurs. The method exploits several spatiotemporal characteristics of electrically-evoked spikes to overcome the challenge of detecting small axonal spikes in extracellular recordings. The algorithm was validated using large-scale ex vivo stimulation and recording experiments in macaque retina, by comparing algorithmically and manually identified bundle activation thresholds. The algorithm could be used in a closed-loop manner by a future epiretinal prosthesis to reduce poorly controlled visual percepts associated with bundle activation. The method may also be applicable to other types of retinal implants and to cortical implants.ContributionsPT developed the algorithm and analyzed the data, with input from SMi and EJC. NB and NS helped with the analysis. SMa and LG performed dissections and collected the data. PT and VFH performed manual identification. PH, AS and AML developed and supported recording hardware and software. PT, EJC and SMi wrote the manuscript. NS and SMa edited it. EJC and SMi supervised the project.

The Use of Computer Guided Tall andTilted Pin Hole Immediately Loaded Implants(TTPHIL) Technique for Severe Atrophic Maxilla Rehabilitation: A One Year Follow-Up

For successful placement of dental implants, the clinician needs adequate bone in three dimensions around endo-osseous implants to enhance Bone Implant Contact (BIC) area and primary stability. The absence of optimum bone calls for complex procedures such as sinus lifts, bone augmentations using grafts that aggravates patient morbidity, dramatically higher costs and limited patient satisfaction. To overcome disadvantages of grafting, graft-less solution used in combination or alone, such as tilted implants, use of long, narrow implants, bi-cortical implants, all-on-4 techniques have enhanced patient acceptance and clinical ease. All-on-4 protocol is one such combination treatment concept whose success has been demonstrated mainly in ideal/moderate osseous structures. Further, it accommodates 10-12 teeth per arch, mostly without second molars compromising chewing efficiency and creating cantilevers especially in rehabilitations opposing complete set of natural teeth. Additionally, optimal number of implants required to support full arch prosthesis remains unclear. Therefore, to circumvent the limitations of all-on-4 technique, 6 long (16-25 mm) and tilted implants have been used to restore 14 teeth in severely atrophic maxillary arch of a healthy 75-year-old female in the following case report. Tall implants engage basal cortical bone aiding in immediate fixation and increase in surface area of osseo-integration. All implants were placed using minimally invasive flapless technique and immediately loaded within 3 days with a screw-retained multiunit DMLS prosthesis. The pterygoid cortex engagement of distal implants does not have any deleterious biomechanical effect eliminating the distal cantilever.

Cortical Implants In Cerebrum - A Review

The cortical implant is neuroprosthetic which is a direct bridging link to the cerebral cortex of the brain. It provides stimulation and has different benefits depending upon the type of design and the placement of the implant. It is a typical cortical with a microelectrode array, a small device that transmits or receives the neural signal. Its main goal is to replace the neural circuitry in the brain that no longer functions properly. It has a wide variety of potential uses from restoring vision to helping patients who suffer from dementia. These implants are placed on the prefrontal cortex. Prefrontal Cortex is helpful in restoring the attention that helps in decision making. These implants act as a replacement that replaces the damaged tissues in the cortex. This review was done based on the articles obtained from various platforms like PubMed, PubMed Central and Google Scholar. They were collected with a restriction on a time basis from 2000 - 2020. The inclusion criteria were original research papers. In vitro, studied among various conditions and articles that contain pros and cons. Exclusion criteria came into account for review articles, retracted articles and articles of other languages. All the articles are selected based on cortical implants in the cerebrum. Cortical implants are placed to replace the neural circuitry in the brain that no longer functions properly. It helps patients with neurological disorders. It helps patients who have difficulty in complex sensory and neural functions. The biggest advantage of neuroprosthesis is that it is directly interfaced with the cortex.

Studying Cortical Plasticity in Ophthalmic and Neurological Disorders: From Stimulus-Driven to Cortical Circuitry Modeling Approaches

Unsolved questions in computational visual neuroscience research are whether and how neurons and their connecting cortical networks can adapt when normal vision is compromised by a neurodevelopmental disorder or damage to the visual system. This question on neuroplasticity is particularly relevant in the context of rehabilitation therapies that attempt to overcome limitations or damage, through either perceptual training or retinal and cortical implants. Studies on cortical neuroplasticity have generally made the assumption that neuronal population properties and the resulting visual field maps are stable in healthy observers. Consequently, differences in the estimates of these properties between patients and healthy observers have been taken as a straightforward indication for neuroplasticity. However, recent studies imply that the modeled neuronal properties and the cortical visual maps vary substantially within healthy participants, e.g., in response to specific stimuli or under the influence of cognitive factors such as attention. Although notable advances have been made to improve the reliability of stimulus-driven approaches, the reliance on the visual input remains a challenge for the interpretability of the obtained results. Therefore, we argue that there is an important role in the study of cortical neuroplasticity for approaches that assess intracortical signal processing and circuitry models that can link visual cortex anatomy, function, and dynamics.